Humidity control sensor for a refrigerator

ABSTRACT

An improved humidity control sensor is provided that cost effectively allows for a more efficient operation of a refrigerator by using two temperature sensors to determine ambient conditions of a room housing the refrigerator. Based on the two temperature sensor measurements, the humidity control sensor may e.g., use a processing device to efficiently control a heating element in thermal communication with an exterior surface of the refrigerator&#39;s cabinet to prevent condensation from forming on that exterior surface.

FIELD OF THE INVENTION

The subject matter of the present disclosure relates generally to an improved humidity control sensor for a refrigerator that can efficiently control a heating element in a refrigerator in a more cost effective manner.

BACKGROUND OF THE INVENTION

Consumer refrigerator appliances are commonly used to keep items such as food at a temperature below the ambient temperature of the room in which the refrigerator is housed. For various reasons, insulation is generally provided between the cooled compartments and the exterior cabinet of the refrigerator. Besides keeping the refrigerated compartments cooled, this also helps prevent the formation of condensation on the exterior surface of the refrigerator's cabinet by keeping it warmer than the refrigerated compartments and ideally warmer than the ambient dew point temperature.

In some areas of a refrigerator, however, it is either impractical or impossible to provide enough insulation to keep the exterior surface of the refrigerator's cabinet above the ambient dew point temperature. This can be an issue in areas such as e.g., the mullion between two refrigerated compartments, and the mullion provided between two French-style doors. Other areas can also be problematic as well.

In an effort to remedy this problem, some refrigerators may provide heating elements in these areas that are in thermal communication with the exterior surface of the refrigerator's cabinet so as to heat the exterior surface above the ambient dew point temperature and prevent condensation from forming. Further, refrigerators may include a humidity control sensor that measures the ambient humidity and uses that measurement to heat the external surface of the refrigerator only when it is required to prevent condensation from forming. Challenges exist with this construction, however, as the humidity sensor can be can be relatively expensive.

Accordingly, an improved humidity sensor for a refrigerator would be useful. More particularly, an economical device that can be used with a refrigerator to measure humidity would be useful. Such a device that can also be used to help efficiently control e.g., a heating element of the refrigerator appliance would also be useful.

BRIEF DESCRIPTION OF THE INVENTION

The present disclosure provides an improved humidity control sensor that cost effectively allows for a more efficient operation of a refrigerator by using two temperature sensors to determine ambient conditions where the refrigerator is located. Based on the two temperature sensor measurements, the humidity control sensor can, for example, provide information to a processing device to efficiently control a heating element in thermal communication with an exterior surface of the refrigerator's cabinet to prevent condensation from forming on that exterior surface. Additional features as described herein may also be added to further improve heat transfer. Methods for operating such a refrigerator are also provided. Additional aspects and advantages of the invention will be set forth in part in the following description, or may be apparent from the description, or may be learned through practice of the invention.

In one exemplary embodiment, the present disclosure provides a refrigerator appliance having a cabinet having an exterior surface, a heating element in thermal communication with the exterior surface of the cabinet, and a humidity control sensor. The humidity control sensor may include a receptacle configured for holding a pool of water and a first temperature sensor configured to measure a wet bulb temperature, wherein the first temperature sensor is positioned at the receptacle so as to provide temperature measurement of the pool of water. The humidity control sensor may also include a second temperature sensor configured to measure a dry bulb temperature and a processing device in communication with the first and second temperature sensors. The processing device may be configured for receiving a first temperature measurement from the first temperature sensor and a second temperature measurement from the second temperature sensor, and controlling the heating element based on the first temperature measurement and the second temperature measurement from the step of receiving.

In one exemplary aspect, the present disclosure provides a method for operating a refrigerator appliance, including providing a refrigerator including a cabinet having an exterior surface, a heating element in thermal communication with the exterior surface of the cabinet, and a humidity control sensor. The humidity control sensor may include a receptacle configured for holding a pool of water and a first temperature sensor configured for measuring a wet bulb temperature, wherein the first temperature sensor is positioned in the receptacle so as to be in the pool of water. The humidity control sensor may also include a second temperature sensor configured to measure a dry bulb temperature, and a processing device in communication with the first and second temperature sensors. The method for operating a refrigerator appliance may also include moving air across the first temperature sensor for a length of time, and measuring the wet bulb temperature after the length of time using the first temperature sensor and the dry bulb temperature using the second temperature sensor. Additionally, the method for operating a refrigerator appliance may include controlling the heating element based on the wet bulb temperature measurement and the dry bulb temperature measurement from the step of measuring.

These and other features, aspects, and advantages of the present disclosure will become better understood with reference to the following description and appended claims. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including the best mode thereof, directed to one of ordinary skill in the art, is set forth in the specification, which makes reference to the appended figures, in which:

FIG. 1 is a front view of an exemplary embodiment of a refrigerator of the present disclosure with its doors open.

FIG. 2 is a front view of another exemplary embodiment of a refrigerator of the present disclosure with its top doors open.

FIG. 3 is a diagram of an exemplary embodiment of a refrigerant based cooling system of the present disclosure.

FIG. 4 is a diagram of an exemplary embodiment of a humidity control sensor of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

Reference now will be made in detail to embodiments of the invention, one or more examples of which are illustrated in the drawings. Each example is provided by way of explanation of the invention, not limitation of the invention. In fact, it will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the scope or spirit of the invention. For instance, features illustrated or described as part of one embodiment can be used with another embodiment to yield a still further embodiment. Thus, it is intended that the present invention covers such modifications and variations as come within the scope of the appended claims and their equivalents.

FIG. 1 is a front view of an exemplary refrigerator 10 depicted as a side by side refrigerator in which an exemplary humidity control sensor of the present disclosure may be utilized. Refrigerator 10 comprises a refrigerated cabinet including an outer case 16, which houses a fresh food storage compartment 12 and a freezer storage compartment 14, with the compartments arranged side-by-side, as well as inner liners 18 and 20. Inner liners 18 and 20 may generally be molded from a suitable plastic material. Outer case 16 is may be formed by folding a sheet of a suitable material, such as pre-painted steel, into an inverted U-shape to form top and side walls of outer case 16. A bottom wall of outer case 16 may be formed separately and attached to the case side walls and to a bottom frame that provides support for refrigerator 10.

A breaker strip 22 may extend between a front flange of outer case 16 and an outer front edge of inner liners 18 and 20. Breaker strip 22 may be formed from a suitable resilient material. The space between inner liners 18 and 20 may be insulated and covered by another strip of suitable resilient material, which also is commonly referred to as a mullion 24. Mullion 24 may have an external surface 25 and may include a heating element 52 in thermal communication with external surface 25 to prevent the formation of condensation, as discussed below.

Heating element 52 may be embedded in the wall of mullion 24 and may be positioned in a zig-zag manner in an effort to provide sufficient heat to all of exterior surface 25. Heating element 52 may be constructed as, e.g., a loop of resistive wire that becomes heated upon the flow of an electrical current therethrough. Additionally, heating element 52 may include a plug (not shown) for connection to a power supply. Breaker strip 22 and mullion 24 may form a front face of the cabinet, and extend completely around the inner peripheral edges of outer case 16 and between inner liners 18 and 20.

A freezer door 42 and a fresh food door 44 close access openings to freezer storage compartment 14 and fresh food storage compartment 12. Each door 42, 44 is mounted by a top hinge and a bottom hinge (not shown) to rotate about its outer vertical axis between an open position, as shown in FIG. 1, and a closed position. To facilitate the storage of items to be refrigerated and/or frozen, freezer door 42 may include a plurality of storage shelves 46 and fresh food door 44 may include a plurality of storage shelves 48. Additionally, fresh food storage compartment 12 may include one or more slide-out drawers 30 and shelves 28 and freezer storage compartment 14 may include one or more shelves 28 or wire baskets 36.

The freezer storage compartment 14 may include an ice compartment 38 and a dispenser 32 provided in freezer door 42 such that ice and/or chilled water can be dispensed without opening the freezer door 42, as is well known in the art. Doors 42 and 44 may be opened by handles 50.

Aspects of the present disclosure may be utilized in appliances having different configurations and constructions as well. FIG. 2 is a front view of an exemplary bottom mount refrigerator 100 in which an exemplary humidity control sensor of the present disclosure may also be utilized. Bottom mount refrigerator 100 has many components similar to those in side by side refrigerator 10. For example, refrigerator 100 may include a cabinet having an outer case 116 and a fresh food storage compartment 112 contained within an inner liner 118. The cabinet may also include a freezer section 114 contained within outer case 116 and an inner liner (not shown). Further, refrigerator 100 may include a breaker strip 122 that may extend between a front flange of case 116 and an outer front edge of inner liner 118. The space between inner liner 118 of fresh food storage compartment 112 and the inner liner of the freezer section 114, may be insulated and covered by a strip of suitable material, forming mullion 124. Mullion 124 may have an external surface 125 and may include a heating element 152 in thermal communication with external surface 125 to prevent the formation of condensation, as discussed below. Heating element 152 may have a similar configuration and construction as heating element 52, discussed above. Breaker strip 122 and mullion 124 form a front face of the cabinet.

Referring still to FIG. 2, fresh food storage compartment 112 may also include slide-out drawers 130 and shelves 128. Fresh food doors 144 and 145 may be rotatably hinged to a vertical edge of outer case 116 for selectively accessing fresh food storage compartment 112, and are rotatable between an open position, as shown in FIG. 2, and a closed position (not shown). Fresh food doors 144 and 145 may also include a plurality of storage shelves 148. In addition, a freezer door 142 is arranged below fresh food doors 144 and 145 for selectively accessing freezer chamber 114. Freezer door 142 may be coupled to a freezer drawer (not shown) slidably mounted within freezer chamber 114.

Mounted to fresh food door 144 is a mullion 154, having an exterior surface 158, and forming part of the cabinet of refrigerator 100. Mullion 154 may be provided to ensure a proper seal is created between doors 144 and 145 and fresh food storage compartment 112. Mullion 154 may be rotatably mounted to door 144, such that when door 144 is open, it is positioned adjacent to door 144 and when door 144 is closed, it is positioned in such a manner as to effectuate a seal between doors 144 and 145 and fresh food storage compartment 112. A mullion guide 156 may be provided to ensure mullion 154 is in its proper position. Mullion 154 may be constructed from any suitable material, and insulation may be provided within it. Mullion 154 may include a heating element 156 in thermal communication with external surface 158 to prevent the formation of condensation, as discussed below. Heating element 156 may have a similar configuration and construction as heating elements 52 and 152, discussed above.

It should be appreciated that refrigerator 10 of FIG. 1 and refrigerator 100 of FIG. 2 are for illustrative purposes only and that the present invention is not limited to any particular type, style, or configuration of refrigerator appliance, and that such appliance may include any manner of refrigerator, freezer, refrigerator/freezer combination, and so forth.

As with known refrigerators, refrigerators 10 and 100 may include a refrigeration system 60, depicted in FIG. 3. Refrigeration system 60 may cool refrigerators 10 and 100 by executing a vapor compression cycle, using components including a compressor 62, a condenser 64, an expansion device 66, and an evaporator 68, each connected in series as a loop and charged with a refrigerant. Evaporator 68 is a type of heat exchanger which transfers heat from air moving over evaporator 68 to the refrigerant flowing through evaporator 68, thereby causing the refrigerant to vaporize and the air moving past evaporator 68 to cool. A fan 212 may be provided to move air past evaporator 68 and into one or more refrigerator and/or freezer compartment(s), cooling the compartment(s). Refrigeration system 60 may be positioned at the rear of the refrigerator's cabinet, behind the refrigerator and/or freezer compartments. The construction and operation of refrigeration system 60 are well known to those skilled in the art.

As discussed previously, one problem that is experienced with some refrigerators is that condensation may form on an exterior surface. This happens when the temperature of the exterior surface falls below a temperature in which the water vapor in the air condenses to a liquid. This temperature is known as the dew point temperature. This problem tends to occur most frequently in areas of the refrigerator where it is impractical or impossible to provide enough insulation to keep the exterior surface from being cooled below the dew point temperature due to heat transfer with the lower temperature in the refrigerator's compartments. For example in refrigerator 10, mullion 24 can be particularly susceptible, and in refrigerator 100, mullion 124 and mullion 154 can each be particularly susceptible.

To remedy this issue, refrigerators may utilize a heating element in the problematic areas to ensure the exterior surface remains above the dew point temperature of the room. However, without factoring in the ambient conditions of the room, the refrigerator will inevitably operate the heating element when it is not required, which can create inefficiencies in use of the refrigerator. This issue has previously been addressed by installing relatively expensive humidity sensors, which are then used as a factor in determining when the heating element should be operated. Accordingly, the present disclosure provides for a cost effective means for controlling a heating element without requiring a relatively expensive humidity sensor.

FIG. 4 provides an exemplary embodiment of a humidity control sensor 200 of the present invention. For this exemplary embodiment, humidity control sensor 200 includes a processing device 214, a first temperature sensor 202, and a second temperature sensor 204. Processing device 214 may include a memory and one or more processors, such as a general or special purpose microprocessor operable to execute programming instructions or micro-control code associated with operation of refrigerator 10 or 100. The memory may represent random access memory, such as DRAM, or read only memory, such as ROM or FLASH. In one embodiment, the processor executes programming instructions stored in memory. The memory may be a separate component from the processor or may be included onboard within the processor.

First temperature sensor 202 may be in communication (shown schematically as line 203) with processing device 214 and configured for measuring the ambient wet bulb temperature of the room in which refrigerator 10 or 100 is housed. In general, the wet bulb temperature is the minimum temperature that may be achieved by pure evaporative cooling of a wetted object in a ventilated area. In order to measure the ambient wet bulb temperature, a receptacle 206 configured for holding a pool of water 208 is provided. Pool of water 208 may be supplied to receptacle 206 by, e.g., a water line 210 connected to a water source, or water generated from a defrost cycle in refrigerator 10 or 100. Defrost cycles are utilized to reduce or remove a buildup of ice on evaporator 68, from refrigeration system 60 in FIG. 3. A refrigerator may use, e.g., electric heaters for the defrost cycle. Water could also be supplied to receptacle 206 from an icemaker in refrigerator 10 of 100 such as e.g., an icemaker in one of the doors, the reservoir of a wet ice/nugget ice system, or from other sources as well.

In order to measure the ambient wet bulb temperature, first temperature sensor 202 may be positioned in receptacle 206 so as to be in pool of water 208, as shown in FIG. 4. Alternatively, a cloth wetted from the pool of water in receptacle 206 may be in contact with first temperature sensor 202. Additionally, fan 212 may be provided to move air past first temperature sensor 202 and/or the pool of water in receptacle 206. Fan 212 may be the same fan used in refrigeration cycle 60 from FIG. 3 to move air past condenser 64. Fan 212 may also be in communication with processing device 214 (shown schematically as line 213), and processing device 214 may be configured to operate fan 212 for a predetermined amount of time before receiving the wet bulb temperature measurement from first temperature sensor 202. Alternatively, processing device 214 may be configured to operate fan 212 for an indeterminate amount of time until the water is at a steady state temperature, or within a predetermined value of steady state temperature.

Second temperature 204 sensor may be in communication with processing device 214 (as shown schematically by line 205) and configured to measure the ambient dry bulb temperature. Second temperature sensor 204 may be positioned anywhere about refrigerator 10 or 100 that allows it to measure the dry bulb temperature of the room in which refrigerator 10 or 100 is housed. Further, first temperature sensor 202 and second temperature sensor 204 may be any type of temperature sensor using electronic signals, such as a thermistor or thermocouple. In another embodiment of the invention, second temperature sensor 204 could be located external of refrigerator 10 or even in another appliance whereby temperature information from sensor 204 is communicated e.g., wirelessly to processing device 214.

Processing device 214 may control heating element 52 of refrigerator 10, or heating elements 152, 156, or both of refrigerator 100 based on the wet bulb temperature measurement from first temperature sensor 202 and the dry bulb temperature measurement from second temperature sensor 204. Refrigerator 10 or 100 may, instead or in addition, have a heating element in thermal communication with any exterior surface of the cabinet, and processing device 214 may control any such heating element based on the wet bulb temperature measurement from first temperature sensor 202 and the dry bulb temperature measurement from second temperature sensor 204.

In still another exemplary embodiment, processing device 214 may calculate the absolute humidity, relative humidity, or both based on the wet bulb and dry bulb temperature measurements from first and second temperature sensors 202 and 204. Processing device 214 may use a chart, such as a psychometric chart, stored in its memory to make the humidity calculation. Additionally, processing device 214 may calculate the ambient dew point temperature of the room in which the refrigerator is housed based on the humidity calculation and the ambient dry bulb temperature measurement. The calculation of dew point temperature from the ambient dry bulb temperature and ambient relative humidity may be done a number of ways known to those of ordinary skill in the art. Thus further details of such calculation are not necessary to enable those of ordinary skill in the art to make use of the present disclosure. Once calculated, processing device 214 may use the relative humidity, absolute humidity, dew point temperature, or a combination thereof to control a heating element in refrigerator 10 or 100. More specifically, using the information provided by temperature sensors 202 and 204, processing device 214 can be configured to determine whether operation of the heating elements is necessary to prevent condensation on an external surface of the refrigerator appliance. If so, processing device 214 can be configured to activate one or more heating elements. In one exemplary embodiment, one or more such heating elements are operated for a predetermined period of time if the processing device determines that ambient conditions will lead to condensation on one or more external surfaces of the refrigerator if such heating elements are not activated.

In yet another exemplary embodiment, humidity control sensor 200 may further include a third temperature sensor 54 in communication with processing device 214 that is configured to measure the temperature of an external surface of the cabinet of refrigerator 10 or 100. Using refrigerator 10 of FIG. 1, for example, processing device 214 may use this temperature measurement to control a heating element 52 in thermal communication with external surface 25 of mullion 24. For example, when the temperature of external surface 25 measured by the third temperature sensor 54 falls within a predetermined value of the calculated dew point temperature, processing device 214 may cause heating element 52 in thermal communication with external surface 25 to activate. Alternatively, processing device 214 may activate heating element 52 based on the relation of the third temperature sensor's 54 measurement to the ambient wet bulb temperature, the ambient dry bulb temperature, or both.

In still another exemplary embodiment, a heating element in thermal communication with the cabinet of refrigerator 10 or 100, such as heating elements 52, 152, and 154, and controlled by processing device 214 may be a variable output heating element. This would allow processing device 214 to choose a higher heat output for some situations, such as when the external surface of the cabinet is within a certain “critical” range of the ambient dew point temperature or below the ambient dew point temperature. In other situations, processing device 214 may choose a lower heating level, such as when the external surface of the cabinet is not within the critical range of the ambient dew point temperature, but still within a predetermined range of the dew point temperature above the critical range.

In yet another exemplary embodiment, humidity control sensor 200 may also be used to improve the timing of the defrost cycle in refrigerator 10 or 100, or to control a water dispenser heater. Additionally, humidity control sensor 200 may wirelessly be in communication with one or more other appliances that may be able to utilize the measurements taken, e.g., a dryer, air conditioner, or thermostat.

This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they include structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 

What is claimed is:
 1. A refrigerator appliance, comprising: a cabinet having an exterior surface, a heating element in thermal communication with the exterior surface of said cabinet; and a humidity control sensor, said humidity control sensor comprising: a receptacle configured for holding a pool of water; a first temperature sensor configured to measure a wet bulb temperature, wherein said first temperature sensor is positioned at the receptacle so as to provide temperature measurement of the pool of water; a second temperature sensor configured to measure a dry bulb temperature; and a processing device in communication with said first and second temperature sensors, said processing device configured for: receiving a first temperature measurement from said first temperature sensor and a second temperature measurement from said second temperature sensor; and controlling the heating element based on the first temperature measurement and the second temperature measurement from said step of receiving.
 2. A refrigerator appliance as in claim 1, wherein said step of controlling further comprises determining a relative humidity, an absolute humidity, a dew point temperature, or combination thereof using the first temperature measurement and the second temperature measurement from said step of receiving.
 3. A refrigerator appliance as in claim 1, further comprising a refrigeration system, said refrigeration system comprising a fan, wherein said processing device is further configured for operating the fan for a predetermined amount of time prior to receiving the wet bulb temperature measurement from said first temperature sensor.
 4. A refrigerator appliance as in claim 1, further comprising a refrigeration system, said refrigeration system comprising a fan, wherein said processing device is further configured for operating the fan until the temperature of the water in said receptacle is within a predetermined range of a steady-state temperature.
 5. A refrigerator appliance as in claim 1, wherein said humidity control sensor further comprises a third temperature sensor in communication with said processing device, wherein said third temperature sensor is configured to measure the temperature of an exterior surface of said cabinet, and wherein said processing device is further configured for heating the exterior surface of said cabinet when the temperature of the exterior surface of said cabinet falls within a predetermined range of the dew point temperature.
 6. A refrigerator appliance as in claim 1, wherein said receptacle is configured to retain water generated from a defrost cycle of the refrigerator appliance.
 7. A refrigerator appliance as in claim 1, wherein said processing device comprises at least one microprocessor, a memory, or both.
 8. A refrigerator appliance as in claim 1, wherein at least one of said first or second temperature sensors is a thermistor.
 9. A refrigerator appliance as in claim 1, wherein said cabinet further comprises: a compartment configured for the storage of items to be refrigerated, said compartment defining a compartment opening; a first door rotatably mounted about a vertical axis adjacent the compartment opening of said compartment; a second door rotatably mounted about a vertical axis adjacent the compartment opening of said compartment, said first door and said second door rotatable between an open position and a closed position; and a mullion having an exterior surface, wherein said mullion is mounted to said first door to form a seal between said first door and second door when they are in the closed position, and wherein the exterior surface of said mullion is in thermal communication with said heating element.
 10. A refrigerator appliance as in claim 1, wherein said cabinet further comprises: a first compartment defining a first compartment opening; a second compartment defining a second compartment opening, said first and second compartments configured for the storage of items to be refrigerated or frozen; a wall separating said first and second compartments; and a mullion positioned at the exterior of said wall and adjacent to the first and second compartment openings of said first and second compartments, wherein said mullion is in thermal communication with said heating element.
 11. A refrigerator appliance as in claim 1, wherein said heating element is a variable output heating element.
 12. A method for operating a refrigerator appliance, comprising: providing a refrigerator comprising a cabinet having an exterior surface, a heating element in thermal communication with the exterior surface of the cabinet, and a humidity control sensor, wherein the humidity control sensor comprises: a receptacle configured for holding a pool of water; a first temperature sensor configured for measuring a wet bulb temperature, wherein the first temperature sensor is positioned at the receptacle so as measure the temperature of the pool of water; a second temperature sensor configured to measure a dry bulb temperature; and a processing device in communication with the first and second temperature sensors; moving air across the first temperature sensor for a length of time; measuring the wet bulb temperature after the length of time using the first temperature sensor and the dry bulb temperature using the second temperature sensor; and controlling the heating element based on the wet bulb temperature measurement and the dry bulb temperature measurement from said step of measuring.
 13. A method for operating a refrigerator appliance as in claim 12, wherein said step of controlling further comprises determining a relative humidity, an absolute humidity, a dew point temperature, or combination thereof using the first temperature measurement and the second temperature measurement from said step of receiving.
 14. A method for operating a refrigerator appliance as in claim 12, wherein the processing device comprises at least one processor, a memory, or both, and wherein the processing device determines the relative humidity, absolute humidity, or both by referencing a chart stored in the memory.
 15. A method for operating a refrigerator appliance as in claim 12, wherein the refrigerator further comprises a refrigeration system, wherein the refrigeration system comprising a fan, and wherein air is moved across the first temperature sensor using the fan.
 16. A method for operating a refrigerator appliance as in claim 12, wherein the humidity control sensor further comprises a third temperature sensor in communication with the processing device, wherein the third temperature sensor is configured for measuring the temperature of an exterior surface of the cabinet, and wherein the processing device is further configured for heating the exterior surface of the cabinet when the temperature of the exterior surface of the cabinet falls within a predetermined range of the dew point temperature.
 17. A method for operating a refrigerator appliance as in claim 12, wherein the heating element is a variable output heating element.
 18. A method for operating a refrigerator appliance as in claim 12, wherein the cabinet further comprises: a compartment configured for the storage of items to be refrigerated, the compartment defining a compartment opening; a first door rotatably mounted about a vertical axis adjacent the compartment opening of the compartment; a second door rotatably mounted about a vertical axis adjacent the compartment opening of the cabinet, the first door and second doors rotatable between an open position and a closed position; and a mullion having an exterior surface, wherein the mullion is mounted to the first door to form a seal between the first and second doors when they are in the closed position, and wherein the exterior surface of the mullion is in thermal communication with the heating element.
 19. A method for operating a refrigerator appliance as in claim 12, wherein the cabinet further comprises: a first compartment defining a first compartment opening and a second compartment defining a second compartment opening, each configured for the storage of items to be refrigerated or frozen; a wall separating the first and second compartments; and a mullion positioned at the exterior of the wall and adjacent to the first and second compartment openings of the first and second compartments, wherein the mullion is in thermal communication with the heating element.
 20. A method for operating a refrigerator appliance as in claim 12, wherein the receptacle is configured to retain water generated from a defrost cycle of the refrigerator appliance. 